I would say it this way: Photoshop does a permanent RelCol conversion on-the-fly from the displayed color space of the image to the monitor profile. I think this makes it more clear. Displayed color space of the image could be the soft proofing color space, if soft proofing is off then the color space of the embedded profile will be used for displaying, and if there is no embedded profile the image will be displayed in the color space of the color profile selected for the working space in the Color preferences.

Is displayed color space different from working space? Can it be any color space, either absolute (synthetic in digitaldog's article) color space or output device (printer or device dependent) color space? Must it be sRGB or monitor (custom) color space?

As for those profiles circled with RED, my understanding is that they are preferred and recommended RGB working spaces. They are grouped for easy and direct accessibility, as icc profile has an internal name which could be different from its actual file name. Those profile names that are appearing in the selection pull-down menu are internal profile names.

With displayed color space I mean the color space the image is being currently displayed in - that's it. In Photoshop there are 3 possible places that control this. In order of priority this is the color profile chosen in the proof setup when the proof colors is on, then the embedded profile of the image, and for images without a profile - the color profile selected for a working space in the Color Settings. So it is not necessarily a working space as defined by Digitaldog because the user can assign any color profile in those 3 places for whatever reasons they want.

...As for those profiles circled with RED, my understanding is that they are preferred and recommended RGB working spaces. ...

Preferred or Recommended, that's another two beautiful names that fit perfectly for the meaning of working spaces as defined by Digitaldog.

edit: or if the meaning of "working spaces" as defined by Digitaldog is already established in the user's community, then Adobe should change the name "Working spaces" in the Color settings to something else. I can't think of a nice name but how about "Special Spaces". I've seen a lot of users on the Internet overrating the importance of the profiles selected for working spaces in the color settings believing that it plays a big role in every image being displayed while the fact is that it only affects the display of untagged images and does nothing to the files unless if set up to function as a conversion tool. I believe that the name of the "Working Spaces" section in the Color Setting adds to this misunderstanding.

Wonder why profile chosen for proof setup has the top priority? It is disable when a image file is read into PS.

Turning Soft proofing on and off does exactly the same as if choosing Edit > Assign to another profile and when done, choose Edit > Assign > to the previous profile - just make sure you don't save before but after reassigning the original profile. So the next time you open the image it is displayed in the color space of the original profile. Soft Proofing simply automates this process and also allows you to save in the middle of proofing without affecting the file.Also soft proofing does the same what the profile selected for a working space in the color settings does to a untagged image, it just displays the image using the color space of the profile on the monitor but doesn't do anything to the file when saving it. Information about soft proofing used is not saved with the file so when you open it again Photoshop can't automatically turn it on back for you and you have to do it manually.

When an image file is read into PS, do you agree that an working profile must be defined before further editing/viewing can be carried out?

If the image file is with a profile, the working profile in the color settings with default color management policy doesn't have any effect on the image and it will be displayed in the color space of the embedded profile. If the image is untagged (without a profile) then it will be displayed in the color space of the working profile. As I said this works the same as soft proofing, it it will not affect the color values in the file but only only in the video card for displaying it. The only difference from soft proofing is if you convert an untagged image to a profile - it will convert from the meaning of the colors as displayed in the color space of the working profile.There is no rules when to changes the working profile in the color settings - it depends on what you want to do but in most cases people prefer to edit the image referring mostly to one color space and occasionally checking how the image looks in other color spaces using soft proofing. You may also make edits or alterations for a specific color space and separate the changes on different layers

NO, soft proofing simulates "Convert to Profile", you can (should) also select the rendering intent when soft proofing. If Soft proofing did what you say, it would be completely useless.

You are completely wrong and it will be completely useless if it does what you say. Soft Proofing as well as Assign Profile does not change the color values in the file but changes the appearance of the colors by altering the values the video card uses to show how the same values will be displayed in different color spaces. Convert to Profile on the other hand changes the values in the file but doesn't change the values used by the video card to display the image which makes the image remains with the same appearance (no color change) but now the image is in another color space. And this is the whole idea behind color management to preserve the color appearance when reproducing the image in different color spaces by properly converting it. If soft proofing does the same as Convert to Profile you should see no difference and thus it will be useless.

If soft proofing does the same as Convert to Profile you should see no difference and thus it will be useless.

The reason you see diferences is because of different color gamuts between profiles (source - destination), white point, black point, and paper white (in case you select to simulate the paper white or paper color). Also the effect of the rendering intent is huge if your image has colors in the source profile that are out of the gamut of the destination profile. Selecting "perceptual" or "relative colorimetric" will make a lot of difference.

The advantage of using Soft Proofing is that you can edit in a well behaved working profile as ProphotoRGB or AdobeRGB and visualize the effect in your desired output profile (example, combination of printer and paper).

Just try to assign an output profile of an inkjet printer to an image and compare to soft proofing and you will convince yourself that soft proofing is not the same as Assign profile

The reason you see diferences is because of different color gamuts between profiles ...

You are still getting it wrong, you should see a difference when Converting to profile only when the destination color space is narrower and only then the rendering intents make sense. When converting to a wider color space there will be no difference. Soft proofing does not simulate Convert to profile. The idea is actually very simple, take for example one color like pure red R=255, G=0, B=0. Display this color without changing its values on different monitors using the monitor's color space or print this color on various printers. The color produced using the same values will appear differently on all these various devices. Soft proofing simulates exactly that.Convert to profile will change the RGB values to another value for each device to reproduce the same color appearance and for devices with narrower color spaces it will try to preserve the color appearance as much as possible.

It will depend on how you use Soft proofing. What you describe is the way it works when you select "Preserve RGB numbers" in the Soft proofing dialog.

IMHO this is not the usual way Soft Proofing is used by photographers.

Yeah, I was talking about soft proofing with Preserve RGB numbers. OK then, I stand corrected and agree with you about all what you said regarding soft proofing - it is useful to soft proof the conversion, so disregard all I said about comparing soft proofing to assign to profile or have in mind that comparison is valid only when Preserve RGB numbers is on. I apologize for the confusion and looking forward to discuss the other issues we've been talking about.

There is nearly zero reason to do this (for RGB). It can be useful for CMYK. I’ll not go into the reasons because this thread is getting a bit too deep and long winded.

Yeah the thread really got too long and winded but since you mentioned nearly zero reason with which I completely agree, I can't resist sharing the fact that I actually am using my soft proofing set to preserve RGB in the recent months working on a web project as a project manager and also being one of the designers. We're currently designing and developing a corporate web site where the use of color in images and html is important for the clients and we decided to calibrate and profile the monitors of the people in charge of approving the project who were in different office locations in town. Since we have wide gamut monitors, by using the monitor color profiles of the clients and soft proofing sRGB values with preserve RGB numbers turned on, we can have a good idea how sRGB images and html colors appear on different monitors used by the people responsible for approving the project. So there it is one of the 0.x reasons to use preserve RGB. I got used to using it this way recently that I forgot to realize that I'm rather a rare exception and gave not very appropriate comparison of soft proofing to Assign to Profile in my previous posts.

Since we have wide gamut monitors, by using the monitor color profiles of the clients and soft proofing sRGB values with preserve RGB numbers turned on, we can have a good idea how sRGB images and html colors appear on different monitors used by the people responsible for approving the project.

Well certainly on your monitor. Others? Their mileage will vary (depending on browser).

+1,rare cases, for example in order to simulate a non-color-managed environment

On YOUR machine. Not others. That’s hardly possible (without the other display, graphic path, profile). You can soft proof how ugly an image will appear using your non color manged app’s or you coulds just load the document and look.

Well certainly on your monitor. Others? Their mileage will vary (depending on browser).

Right, having their monitor profiles and knowing what browser they use, we can only check how a certain group of people see the design with sRGB and html colors on their monitors and that was most important to us. We have no control over what the rest of the people on the internet will see.

Right, having their monitor profiles and knowing what browser they use, we can only check how a certain group of people see the design with sRGB and html colors on their monitors and that was most important to us.

If I'm understanding the task correctly,you have your images in sRGB, you have the monitor profiles of your client(s),but what precisely do you do then in Photoshop ?

I think what the client(s) will see on their monitor (in a html non-color-managed environment) can not be simulatedwith your computer, software and monitor when the monitor is different enough.

Monitor profiles are not only descriptive (e.g. regarding R/G/B primaries),but also corrective (e.g. regarding R/G/B TRCs). So you finally need the device - the client's monitor, to see what comes out.

I think what the client(s) will see on their monitor (in a html non-color-managed environment) can not be simulatedwith your computer, software and monitor when the monitor is different enough.

A monitor color profile can be used in the same way as any other device color profile like printers for example. Photoshop can display how the image will be reproduced on the other device. Soft proofing with RGB numbers preserved, displays how the color values will be reproduced with the other device, and without RGB numbers preserved, displays how the converted values will be reproduced with the other device.